1343688 - WebExtension: devicePixelRatio in background page is always 1

Status: RESOLVED DUPLICATE of bug 1798213

(WebExtensions :: General, defect, P3)

Description

[Niklas Gollenstede]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:52.0) Gecko/20100101 Firefox/52.0
Build ID: 20170223185858

Steps to reproduce:

1. Load any WebExtension
2. Open its debugger via 'about:debugging'
3. Enter 'devicePixelRatio' [enter] in the console


Actual results:

It returns '1', regardless of the screen setup.


Expected results:

It should return the actual devicePixelRatio.

If multiple displays with different dprs are connected, it should probably return the maximum, or that of the primary display.

Comment 1

[Niklas Gollenstede]

This is especially relevant because the positioning of windows with the `browser.window` API expects scaled CSS px values, not the native device pixels. I imagine this can cause some very confusing bugs if the add-on dev doesn't happen to have a devicePixelRatio other than 1 themselves.
The global `screen` object also has unscaled values, so it isn't even possible to reliably create a window that covers say half the screen or is centered.

On my phone on the other hand the devicePixelRatio is reported correctly even in the background page. The `screen` object however contains unscaled values too, which is incorrect here.

Another use-case I have found that needs the correct devicePixelRatio is loading images in the native resolution so they don't look blurry.

Comment 2

[Firefox Bug Husbandry Bot]

Bulk move of bugs per https://bugzilla.mozilla.org/show_bug.cgi?id=1483958

Comment 3

[Gregory Pappas [:gregp]]

Resolving as a duplicate of bug 1798213. We can reopen if you think this is a mistake.